A selective and sensitive high-performance liquid chromatographic method with coulometric detection is described for the quantitation of buspirone and its active metabolite, 1-(2-pyrimidinyl)piperazine, in plasma samples of mice treated orally with buspirone (10 mg/kg body weight). The analytes are extracted with a carboxylic acid solid-phase extraction column before chromatography. A dual-electrode electrochemical detector is used. The limit of detection is 50 pg for buspirone and 35 pg for 1-(2-pyrimidinyl)piperazine.